Conventionally, as for a technique of detecting a traffic light ahead of a vehicle when multiple traffic lights are ahead of the vehicle, a technique of detecting a traffic light with the largest size on image data has been known (for example, see Japanese Patent Application Publication No. 2007-257299).
However, in the technique described in Japanese Patent Application Publication No. 2007-257299), when the view of the largest traffic light is obstructed by an object such as a vehicle ahead, a detection target is forced to be switched to the next-largest traffic light even if the obstruction is temporary. This makes it difficult to properly select a traffic light for a detection target in some cases.